Rezeptorszintigraphie mit 111In-Pentetreotid beiendokrinen gastroenteropankreatischenTumoren

Characterization of 111In-labeled Glucose-Dependent Insulinotropic Polypeptide as a Radiotracer for Neuroendocrine Tumors

Somatostatin receptor targeting is considered the standard nuclear medicine technique for visualization of neuroendocrine tumors (NET). Since not all NETs over-express somatostatin receptors, the search for novel targets, visualizing these NETs, is ongoing. Many NETs, expressing low somatostatin receptor levels, express glucose-dependent insulinotropic polypeptide (GIP) receptors (GIPR). Here, we evaluated the performance of [Lys³⁷(DTPA)]N-acetyl-GIP_1-42, a newly synthesized GIP analogue to investigate whether NET imaging via GIPR targeting is feasible. Therefore, [Lys³⁷(DTPA)]N-acetyl-GIP_1-42 was radiolabeled with ¹¹¹In with specific activity up to 1.2 TBq/µmol and both in vitro and in vivo receptor targeting properties were examined. In vitro, [Lys³⁷(¹¹¹In-DTPA)]N-acetyl-GIP_1-42 showed receptor-mediated binding to BHK-GIPR positive cells, NES2Y cells and isolated islets. In vivo, both NES2Y and GIPR-transfected BHK tumors were visualized on SPECT/CT. Furthermore, co-administration of an excess unlabeled GIP_1-42 lowered tracer uptake from 0.7 ± 0.2%ID/g to 0.6 ± 0.01%ID/g (p = 0.78) in NES2Y tumors and significantly lowered tracer uptake from 3.3 ± 0.8 to 0.8 ± 0.2%ID/g (p = 0.0001) in GIPR-transfected BHK tumors. In conclusion, [Lys³⁷(¹¹¹In-DTPA)]N-acetyl-GIP_1-42 shows receptor-mediated binding in various models. Furthermore, both GIPR-transfected BHK tumors and NES2Y tumors were visible on SPECT/CT using this tracer. Therefore, [Lys³⁷(¹¹¹In-DTPA)]N-acetyl-GIP_1-42 SPECT seems promising for visualization of somatostatin receptor negative NETs.

68Ga-labelled exendin-3, a new agent for the detection of insulinomas with PET

Purpose

Insulinomas are neuroendocrine tumours derived from pancreatic β-cells. The glucagon-like peptide 1 receptor (GLP-1R) is expressed with a high incidence (>90%) and high density in insulinomas. Glucagon-like peptide 1 (GLP-1), the natural ligand of GLP-1R, is rapidly degraded in vivo. A more stable agonist of GLP-1R is exendin-3. We investigated imaging of insulinomas with DOTA-conjugated exendin-3 labelled with ⁶⁸Ga.

Methods

Targeting of insulinomas with [Lys⁴⁰(DOTA)]exendin-3 labelled with either ¹¹¹In or ⁶⁸Ga was investigated in vitro using insulinoma tumour cells (INS-1). [Lys⁴⁰(¹¹¹In-DTPA)]Exendin-3 was used as a reference in this study. In vivo targeting was investigated in BALB/c nude mice with subcutaneous INS-1 tumours. PET imaging was performed using a preclinical PET/CT scanner.

Results

In vitro exendin-3 specifically bound and was internalized by GLP-1R-positive cells. In BALB/c nude mice with subcutaneous INS-1 tumours a high uptake of [Lys⁴⁰(¹¹¹In-DTPA)]exendin-3 in the tumour was observed (33.5 ± 11.6%ID/g at 4 h after injection). Uptake was specific, as determined by coinjection of an excess of unlabelled [Lys⁴⁰]exendin-3 (1.8 ± 0.1%ID/g). The pancreas also exhibited high and specific uptake (11.3 ± 1.0%ID/g). High uptake was also found in the kidneys (144 ± 24%ID/g) and this uptake was not receptor-mediated. In this murine tumour model optimal targeting of the GLP-1R expressing tumour was obtained at exendin doses ≤0.1 µg. Remarkably, tumour uptake of ⁶⁸Ga-labelled [Lys⁴⁰(DOTA)]exendin-3 was lower (8.9 ± 3.1%ID/g) than tumour uptake of ¹¹¹In-labelled [Lys⁴⁰(DTPA)]exendin-3 (25.4 ± 7.2%ID/g). The subcutaneous tumours were clearly visualized by small-animal PET imaging after injection of 3 MBq of [Lys⁴⁰(⁶⁸Ga-DOTA)]exendin-3.

Conclusion

[Lys⁴⁰(⁶⁸Ga-DOTA)]Exendin-3 specifically accumulates in insulinomas, although the uptake is lower than that of [Lys⁴⁰(¹¹¹In-DTPA)]exendin-3. Therefore, [Lys⁴⁰(⁶⁸Ga-DOTA)]exendin-3 is a promising tracer to visualize insulinomas with PET.

Carcinoid of the ampulla of Vater

Endocrine neoplasms only rarely occur at the ampulla of Vater, comprising mostly carcinoids and malignant carcinoids, as well as few cases of poorly differentiated endocrine carcinomas (small cell carcinomas). Only 105 cases are reported in the literature, most as single case reports. For many years, the neoplasms of the disseminated neuroendocrine cell system of the gastrointestinal tract have been subsumed as 'carcinoids'. Instead, in the latest World Health Organization (WHO) classification published in 2000, it is recommended to distinguish between (i) well-differentiated endocrine tumors (carcinoids); (ii) well-differentiated endocrine carcinomas (malignant carcinoids); and (iii) poorly differentiated endocrine carcinomas (small cell carcinomas). Patients with carcinoid tumors of the ampulla of Vater are very often free of clinical and laboratory findings that belong to the carcinoid syndrome. Approximately 26% of all patients with carcinoid tumor reported in the literature had neurofibromatosis. Besides endoscopic retrograde cholangiopancreatography, endosonography, computed tomography or magnetic resonance imaging may complete the staging approach of this tumor. The Kausch-Whipple procedure or pylorus-preserving pancreaticoduodenectomy is considered the treatment of choice for ampullary, well-differentiated carcinoids >2.0 cm and for ampullary neuroendocrine carcinomas. However, it should be considered that long-term survival of patients with ampullary carcinoids is also reported after local tumor excision (5-year survival rate of 90%). The dilemma is that the differentiation of neuroendocrine tumors cannot be assessed intraoperatively in most cases. Therefore, considering that the 5-year survival rate in patients with neuroendocrine carcinomas of the ampulla of Vater is very low without radical resection, neuroendocrine tumors of the ampulla of Vater without definite histological differentiation should undergo extended surgery.

[Clinical value of somatostatin receptor scintigraphy. Studies of pre- and intraoperative localization of gastrointestinal and pancreatic tumors]

BACKGROUND

[111In-DTPA-D-Phe1]-pentetreotide scintigraphy is able to detect neuroendocrine tumors not shown by radiological methods.

PATIENTS AND METHODS

In 270 patients with neuroendocrine gastroenteropancreatic tumors (GEP tumors) 400 somatostatin receptor scintigraphies were performed. 70 patients (38 female, 32 male, aged 28 to 74 [56 +/- 12.6] years) underwent surgery and follow-up over 2 years. The aim of the present study was the comparison of preoperative somatostatin receptor scintigraphy with radiological methods (sonography, CT) and intraoperative localization of GEP tumors with a hand-held gamma-probe.

RESULTS

Somatostatin receptor scintigraphy was successful in localizing primary tumors in all patients. Liver- and lymph node metastases could be visualized with a sensitivity of 94 and 95 percent. In 7 patients 35 lesions could be identified by intraoperative tumor localization using a hand held gamma probe. Radiological methods identified only 11, surgical palpation 15 and preoperative somatostatin receptor scintigraphy 27 lesions.

CONCLUSION

Somatostatin receptor scintigraphy improves detection of small and occult GEP tumors. Intraoperative probe counting with a hand-held gamma probe can identify tumors even when they are small and impalpable, but receptor positive.